Abstract

The major routes of metabolic activation of dibenz[a,h]-anthracene (DBA) have been studied in transformable C3H10T1/2CL8 (C3H10T1/2) mouse embryo fibroblasts in culture. The morphological transforming activities of three potential intermediates formed by metabolism of DBA by C3H10T1/2 cells, trans-3,4-dihydroxy-3,4-dihydro-DBA-(DBA-3,4-diol), trans-dihydroxy-3,4-dihydro-DBA-anti-1,2-oxide (DBA-3,4-diol-1,2-oxide) and DBA-5,6-oxide were determined. DBA-3,4-diol-1,2-oxide was a strong morphological transforming agent giving a mean of 73% dishes with Type II or III foci and 1.63 Type II and III foci per dish at 0.5 microgram/ml. DBA-3,4-diol produced a mean of 42% dishes with Type II or III foci and 0.81 Type II and III foci per dish at 2.5 micrograms/ml. DBA gave a mean of 24% dishes with Type II or III foci and 0.29 Type II and III foci per dish at 2.5 micrograms/ml. DBA-5,6-oxide was found to be inactive. DNA adducts of DBA, DBA-3,4-diol, DBA-3,4-diol-1,2-oxide, DBA-1,4/2,3-tetrol and DBA-5,6-oxide in C3H10T1/2 cells were analyzed by 32P-postlabeling method. DBA gave 11 adducts, nine of which were observed in the DNA of cells treated with DBA-3,4-diol and seven from cells treated with DBA-3,4-diol-1,2-oxide. Two of these adducts that appear in each of the treatment groups have been identified as the product of the interaction of DBA-3,4-diol-1,2-oxide with 2'-deoxyguanosine. Furthermore, there is evidence for DBA-DNA adducts in cells treated with DBA, DBA-3,4-diol and DBA-3,4-diol-1,2-oxide arising from metabolism to (+,-)-trans,trans-3,4,10,11-tetrahydroxy-3,4,10,11-tetrahydro-DBA (DBA-3,4,10,11-bis-diol). These results are based on co-migration of C3H10T1/2 DNA adducts with skin DNA adducts formed after topical treatment of mice with DBA-3,4,10,11-bis-diol. In C3H10T1/2 cells, DBA is metabolically activated through DBA-3,4-diol, which is further activated via the DBA-3,4-diol-1,2-oxide and DBA-3,4,10,11-bis-diol pathways. No evidence is provided for the metabolism of DBA by the K-region pathway.